I'm furious at seller not selling item

Well shoot - that would really tick me off too. You're kind of in a unique position here, in that eBay does not endorse services that AS provides. Sniping is not actually AGAINST eBay policy, but they don't endorse it nevertheless, so don't expect eBay to sympathize with you. So here's what I would do:

1)send an email to that 'seller' advising him that he needs to go through the proper channels to cancel, if he decides to do this again in the future. He will find most anything on eBay's 'Site Map'.

2)do NOT send any money to them - simply 'close out' the auction by going through the screens to pay an alternate method such as snail mail.

3)contact AS about this dilemma- maybe you can get a refund for the false winning bid.

4)be diplomatic in your correspondence with the 'seller', remember that they can now leave you feedback, and retaliatory feedback they may leave you will be the salt on the wound...

You're stuck with your loss. DON'T send them money, or you will get what is in the description!! eBay will be just fine with letting them keep your money as long as he delivers what is described... Nothing. ( cuz it was that way when you bid)

One of the problems with sniping thru a service... you're not notified of a change in the description. The only way around this is to place (or let someone else place) an early lowball bid. You can't change (but can add to) the description after there has been a bid without cancelling all bids first.

I wouldn't even bother contacting them. IMO you're just out of luck...

Yes, I agree about contacting AS. File a support case and explain. They will no doubt give you a credit for the false win.